The objectives of the Subject core are to: 1) recruit 200 rigorously diagnosed high functioning autistic subjects over the 5 year period of study, 2) recruit 200 individually matched normal controls who have a negative personal and family history of developmental and neuropsychiatric disorders, plus 10 additional normal controls of average IQ for the longitudinal study, 3) characterize autistic subjects in terms of the most likely clinical indicators of four separate genetic subgroups (family history of "lesser variant" of autism, family history of mood disorder or anxiety disorder, regression as mode of autism onset, and elevated peripheral serotonin levels), 4) administer the neuropsychologic and cognitive psychology testing from Projects I and II, and 5) provide behavioral management and support for all subjects during fMRI and laboratory eye movement procedures in Projects II and III.